In one form of drive belt, the longitudinally extending belt body is provided with a plurality of longitudinally spaced inner teeth. Such teeth are conventionally provided for a number of different purposes, such as for providing improved flexibility of the belt, permitting it to be utilized with relatively small diameter pulleys, and in certain applications, the teeth are utilized to provide a positive drive, such as drive synchronization is desirable.
A serious problem has arisen in connection with such toothed belts in that the teeth are subjected to relatively high transmissive stresses which tend to cause cracking and shearing of the teeth relative to the belt body. Such deterioration is aggravated by load conditions, such as high speed operation, heavy loading forces, subjection to relatively high temperatures, and subjection to moisture and flooding conditions.
One attempted solution to the vexatious cracking and shearing problem has been to provide a fabric cloth of wooly processed polyamide fibers, or a woven cloth and knit cloth of low oriented polyester fibers, with an elongation of more than 80% as a surface fabric on the toothed portion of the belt. It has been found, however, that such cloths tend to become fatigued and worn, and as a result of the deterioration thereof, fail to prevent the shearing and cracking of the teeth resulting from the repeated engagement of the teeth with the toothed pulleys in the use of the belt. Such deterioration has been found to have been aggravated by the low hydrolysis resistance thereof where the belt is subjected to moisture or flooding in use, and also to be aggravated by the subjection of the thusly fabric-coated belt to high temperatures.
Thus, the fabric-covered toothed belts of the prior art have not had satisfactory long troublefree life and the vexatious problem of cracking and shearing has not been heretofore satisfactorily resolved.